Laminate catheter balloons with additive burst strength and methods for preparation of same

ABSTRACT

A laminate balloon comprising at least two layers of separately oriented thermoplastic polymer material, which are coextensive over the body of the balloon. The two layers may be made of different polymer materials, including an underlying layer made of a low compliant, high strength polymer, such as PET, and an overlying layer of a softer and more flexible polymer material relative to the first polymer material, such as a polyester-polyether block copolymer. The balloon structures have an additive burst pressure, meaning that they are stronger than a single-layer reference balloon corresponding to the underlying polymer layer. The balloons are characterized by a combination of flexibility and surface softness which allows catheters to track down into lesions relatively easily, puncture resistance, abrasion resistance and refoldability, in addition to low compliance and high burst strength. The balloons may be prepared with generally linear or with stepped compliance profiles. Methods of preparation of such balloons are also disclosed.

BACKGROUND OF THE INVENTION

Balloons mounted on the distal ends of catheters are widely used inmedical treatment. The balloon may be used to widen a vessel into whichthe catheter is inserted or to force open a blocked vessel. Therequirements for strength and size of the balloons vary widely dependingon the balloon's intended use and the vessel size into which thecatheter is inserted. Perhaps the most demanding applications for suchballoons are in balloon angioplasty in which catheters are inserted forlong distances into extremely small vessels and used to open stenoses ofblood vessels by balloon inflation. These applications require extremelythin walled, high strength, relatively inelastic balloons of predictableinflation properties. Thin walls are necessary because the balloon'swall and waist thicknesses limit the minimum diameter of the distal endof the catheter and therefore determine the limits on vessel sizetreatable by the method and the ease of passage of the catheter throughthe vascular system. High strength is necessary because the balloon isused to push open a stenosis and so the thin wall must not burst underthe high internal pressures necessary to accomplish this task. Theballoon must have some elasticity so that the inflated diameter can becontrolled, enabling the surgeon to vary the balloon's diameter asrequired to treat individual lesions, but that elasticity must berelatively low so that the diameter is easily controllable. Smallvariations in pressure must not cause wide variation in diameter.

The compliance characteristics of angioplasty balloon materials aredescribed in U.S. Pat. No. 5,447,497, incorporated herein by reference.A variety of low-compliant materials have been employed in angioplastyballoons, including polypropylene, polyimides, polyamides, andpolyesters, such as PET and PEN. Such low compliant materials cangenerally be fabricated into higher strength balloons than balloons madeof more compliant materials. The use of low compliant materials,however, has been associated with a number of minor but undesirableproblems, such as poor refold characteristics, pinhole development,difficulty in bonding to the catheter structure and high frictioncoefficient.

To address some of these problems a number of balloon structures havebeen proposed in which a layer of low compliant polymer material iscoated or coextruded with an over or underlying layer of another polymermaterial less prone to one or more of the problems occasionallyencountered with low compliant balloons. Exemplary of this approach areU.S. Pat. No. 5,270,086 (Hamlin), U.S. Pat. No. 5,195,969 (J. Wang, etal.) and U.S. Pat. No. 5,290,306 (Trotta, et al), which pertain toco-extruded structures and U.S. Pat. No. 5,490,839 (L. Wang, et. al)which pertains to coated balloon structures wherein the balloon coatingimparts refold and soft pliable surface characteristics. The balloons ofthese references are unitary structures whose compliance and burstprofiles are determined primarily by the non-compliant polymer layer,with little or no contribution by the second polymer layer. However,balloons made from coextruded tubes with soft polymer material on thetop layer do provide rewrap, abrasion and puncture resistance, andreduced tracking resistance.

It is also known to prepare catheter balloon structures which includetwo separate concentrically arranged balloon elements mounted on acatheter. References which describe such structures include U.S. Pat.No. 4,608,984, in which an outer balloon element of a highly elasticmaterial such as latex having a deflated circumference less than thediameter of the associated catheter is disclosed for use in refoldingthe inner working balloon after it has been inflated and deflated; andU.S. Pat. No. 5,447,497, U.S. Pat. No. 5,358,487 and U.S. Pat. No.5,342,305, in which a non-linear compliance curve is obtained from twodifferent sized balloon elements or from use of an inner balloon whichbursts at some pressure below the burst pressure of the outer element.The dual concentric balloon structures, are made of materials of quitedifferent strength characteristics and tend to give balloons whose burststrength is little different from to the burst strength of the strongestmember element (typically PET or nylon).

SUMMARY OF THE INVENTION

This invention will provide a linear and noncompliant balloon expansioncurves. In the case both balloons have almost the same diameters.

In one aspect the invention comprises a laminate balloon comprising atleast two layers of separately oriented thermoplastic polymer material,which are coextensive over the body of the balloon. The two layers arepreferably made of different polymer materials. Suitably, the layers aresufficiently adherent to each other so that the laminate balloon is aunitary structure even when the balloon is deflated. Most preferably theballoon has an underlying layer made of a low compliant, high strengthpolymer and an overlying layer of a softer and more flexible polymermaterial relative to the first polymer material. The inventive balloonstructures have an additive burst pressure, meaning that they arestronger than a first single-layer reference balloon corresponding tothe underlying polymer layer. The additive strength of the balloons ofthe invention is exhibited typically by burst strengths greater than thefirst reference balloon by at least 50%, and commonly at least 75%, ofthe strength of a second single-layer reference balloon corresponding tothe overlying relatively soft flexible polymer layer. Optimal balloonsof the invention give burst strengths which exceed the strength of thefirst reference balloon by about 100% or even more of the strength ofthe second reference balloon.

The preferred inventive balloons have good flexibility and surfacesoftness, allowing catheters to track down into lesions relativelyeasily, good puncture resistance, good abrasion resistance and goodrefold characteristics, all contributed by the soft material top layer.Furthermore they also have a low compliance profile with a burststrength which exceeds the strongest PET angioplasty balloons currentlycommercially available.

A second aspect of the invention comprises a preferred method of makinga laminate balloon which includes the steps of

a) providing a first tubing segment of a first polymer material;

b) stretching the first tubing segment at a first stretch ratio toproduce a first stretched tube having an outer diameter;

c) providing a second tubing segment of a second polymer material havingan inner diameter greater than the outer diameter of the first stretchedtube;

d) inserting the first stretched tube into the second tubing segment;

e) stretching the second tubing segment at a second stretch ratio toproduce a second stretched tube, the first and second stretched tubesbeing brought into direct annular contact during the stretching of saidsecond tubing segment, to form a laminate stretched tubing structure;and

f) forming the laminate balloon by pressurizing the laminate stretchedtubing structure at a temperature and pressure above ambient so as toexpand the laminate stretched tubing structure.

A still further aspect of the invention is an alternative process forforming a laminate balloon which includes the steps of:

a) providing a first tubing segment of a first polymer material;

b) stretching the first tubing segment at a first stretch ratio toproduce a first stretched tube;

c) blowing the first stretched tube in a mold to produce a first layerstructure, said first layer structure including waist, cone and bodyportions, the waist portion having an inner diameter;

c) providing a second tubing segment of a second polymer material;

d) stretching the second tubing segment at a second stretch ratio toproduce a second stretched tube having an outer diameter less than theinner diameter of the waist portion of said first layer structure;

e) inserting the second stretched tube into the first layer structureand

f) forming the laminate balloon by pressurizing the second stretchedtube at a temperature and pressure above ambient to expand the secondlayer tube, forming a second layer which is in direct annular contactwith the first layer structure.

Balloons of the invention ordinarily have generally linear compliancecurves, however, if desired, the balloons can be provided with steppedcompliance curves can be prepared by use of a post-blowing annealingprocess to shrink the balloon.

Further aspects of the invention will become apparent from the followingdescription, claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 depict various stages in the preferred process for forming aballoon of the invention.

FIG. 1 is a side plan view of a portion of an extruded tubing segmentfor use in forming a first layer of the inventive balloon according tothe preferred process of the invention.

FIG. 2 is a side plan view of the portion of tubing depicted in FIG. 1after it has been stretched to form the first stretched tube.

FIG. 3 is a cross-sectional view showing the first stretched tube ofFIG. 2 inserted into a second tubing segment.

FIG. 4 is a cross-sectional view as in FIG. 3 after the second tubingsegment has been stretched down onto the first stretched tube.

FIG. 5 is a side sectional view of a balloon of the invention.

FIG. 6 is a graph of the compliance curve of a balloon prepared inaccordance with Example 5.

FIG. 7 is a graph of the compliance curve of a balloon prepared inaccordance with Example 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the preferred embodiments the balloon is formed of two layers ofdifferent polymer material, one of which is a low compliant, highstrength thermoplastic polymer and the other of which is a relativelysoft and flexible polymer material. However, other combinations ofpolymer materials can also be used, including dual layers of the samepolymer material. Furthermore, balloons of the invention can also beprepared using more than two laminae without departing from theprinciples of the invention hereof.

The materials used for strong layer are low compliant, high strengththermoplastic polymers. Suitably the balloon polymer is poly(ethyleneterephthalate) (PET) of initial intrinsic viscosity of at least 0.5,more preferably 0.7-1.3, as reported by the polymer manufacturer. Otherhigh strength polyester materials, such as poly(ethylenenapthalenedicarboxylate) (PEN); polyamides such as nylon 11, nylon 12and aromatic/aliphatic polyamides; thermoplastic polyimides; liquidcrystal polymers and high strength engineering thermoplasticpolyurethanes such as Isoplast 301 sold by Dow Chemical Co., areconsidered suitable alternative materials. Physical blends andcopolymers of such materials may also be used. Examples of thermoplasticpolyimides are described in T. L. St. Clair and H. D. Burks,"Thermoplastic/Melt-Processable Polyimides," NASA Conf. Pub. #2334(1984), pp. 337-355. A suitable thermoplastic polyimide is described inU.S. Pat. No. 5,096,848 and is available commercially under thetradename Aurum® from Mitsui Toatsu Chemicals, Inc., of Tokyo, Japan.Examples of liquid crystal polymers include the products Vectra® fromHoechst Celanese, Rodrun® from Unitika, LX or HX series polymers fromDuPont and Xydar from Amoco. Suitably the liquid crystal polymermaterials are blended with another thermoplastic polymer such as PET.

The soft materials used for soft and flexible layer are suitablythermoplastic elastomers, especially segmented polyester/ether blockcopolymers, such as available under the trademarks Arnitel® and Hytrel®;flexible polyurethanes, such as sold under the trademark Pellethane®;and polyamide/ether block copolymers, such as sold under the Pebax®trademark.

The preferred balloons of the invention are polyester/polyethersegmented block copolymers. Such polymers are made up of at least twopolyester and at least two polyether segments.

The polyether segments of the polyester/polyether segmented blockcopolymers are aliphatic polyethers having at least 2 and no more than10 linear saturated aliphatic carbon atoms between ether linkages. Morepreferably the ether segments have 4-6 carbons between ether linkages,and most preferably they are poly(tetramethylene ether) segments.Examples of other polyethers which may be employed in place of thepreferred tetramethylene ether segments include polyethylene glycol,polypropylene glycol, poly(pentamethylene ether) and poly(hexamethyleneether). The hydrocarbon portions of the polyether may be optionallybranched. An example is the polyether of 2-ethylhexane diol. Generallysuch branches will contain no more than two carbon atoms. The molecularweight of the polyether segments is suitably between about 400 and2,500, preferably between 650 and 1000.

The polyester segments are polyesters of an aromatic dicarboxylic acidand a two to four carbon diol. Suitable dicarboxylic acids used toprepare the polyester segments of the polyester/polyether blockcopolymers are ortho-, meta- or para- phthalic acid,napthalenedicarboxylic acid or meta-terphenyl-4,4'-dicarboxylic acids.Preferred polyester/polyether block copolymers are poly(butyleneterephthalate)-block-poly(tetramethylene oxide) polymers such as AmitelEM 740, sold by DSM Engineering Plastics. Hytrel polymers, sold byDuPont which meet the physical and chemical specifications set outherein can also be used.

Polyamide/polyether block copolymers may also be used as the soft layerpolymer. The polyamide/polyether block copolymers are commonlyidentified by the acronym PEBA (polyether block amide). The polyamideand polyether segments of these block copolymers may be linked throughamide linkages, however, most preferred are ester linked segmentedpolymers, i.e. polyamide/polyether polyesters. Suchpolyamide/polyether/polyester block copolymers are made by a moltenstate polycondensation reaction of a dicarboxylic polyamide and apolyether diol. The result is a short chain polyester made up of blocksof polyamide and polyether. The polyamide and polyether blocks are notmiscible. Thus the materials are characterized by a two phase structure:one is a thermoplastic region that is primarily polyamide and the otheris elastomer region that is rich in polyether. The polyamide segmentsare semicrystalline at room temperature. The generalized chemicalformula for these polyester polymers may be represented by the followingformula: ##STR1## in which PA is a polyamide segment, PE is a polyethersegment and the repeating number n is between 5 and 10.

The polyamide segments are suitably aliphatic polyamides, such as nylons12, 11, 9, 6, 6/12, 6/11, 6/9, or 6/6. Most preferably they are nylon 12segments. The polyamide segments may also be based on aromaticpolyamides but in such case significantly lower compliancecharacteristics are to be expected. The polyamide segments arerelatively low molecular weight, generally within the range of500-8,000, more preferably 2,000-6,000, most preferably about3,000-5,000.

The polyether segments are the same as previously described for thepolyester/polyether segmented block copolymers block copolymers usefulin the invention.

The weight ratio of polyamide to polyether in the polyamide/polyetherpolyesters used in the invention desirably should be in the range of50/50 to 95/5, preferably between 60/30 and 95/5, more preferably,between 70/30 and 92/8.

Polyamide/polyether polyesters are sold commercially under the Pebax®trademark by Atochem North America, Inc., Philadelphia Pa. Examples ofsuitable commercially available polymers are the Pebax® 33 seriespolymers with hardness 60 and above, Shore D scale, especially Pebax®7233, 7033 and 6333. These polymers are made up of nylon 12 segments andpoly(tetramethylene ether) segments in different weight ratios andsegment lengths.

It is also possible to use other PEBA polymers with the physicalproperties specified herein and obtain similar compliance, strength andsoftness characteristics in the finished balloon.

It is preferred that the block copolymers have a hardness, Shore Dscale, of at least 60 and a flexural modulus of no more than about150,000, in order to obtain optimal strength, compliance and softnesscharacteristics. Preferably the Shore D hardness is in the range of65-75 and the flexural modulus is in the range of 50,000-120,000. Thepreferred polymers useful in the invention are also characterized by ahigh ultimate elongation of about 300% or higher and an ultimate tensilestrength of at least 6,000 psi

The preferred process of forming balloons of the invention will bedescribed with reference to FIGS. 1-5.

Referring to FIG. 1 there is shown an extruded tubing segment 12,preferably made of a strong non-compliant material, such as PET. Thetubing segment 12 is stretched longitudinally, typically at an elevatedtemperature, in conventional manner for PET balloons to produce anelongated stretched tube 13 shown in FIG. 2. The stretch ratio is onewhich will provide good strength properties in the blown balloon. Atypical stretch ratio for a PET material is about 1.5-6 times the lengthof the original extruded length. An extruded segment 14 of the secondpolymer material, suitably a polyester/polyether block copolymer, isthen provided having an ID greater than the OD of stretched tube 13.Tube 13 is inserted into tube 14 as shown in FIG. 3. Preferably withoutfurther stretching of the tube 13, tube 14 is stretched to produce asecond stretched tube 15 whose ID is necked down, bringing tube 15 intodirect contact with tube 13, as shown in FIG. 4. For the preferredembodiment a "cold-neck" (i.e. at or below ambient temperature) stretchat a ratio of 3-6 may be employed for this step. The composite tubingstructure shown in FIG. 4 is then blown at elevated pressure in a mannerconventional for single layer balloons, for instance by a process asdescribed in WO 95/22367. The resulting laminate balloon 20, depicted inFIG. 5 has two intimately contacting layers, the inner layer 16 beingPET and the outer layer 17 being the polyester/polyether block copolymermaterial. Although they can easily be pealed apart when the balloon isdissected, layers 16 and 17 are sufficiently adherent that the balloon20 is a unitary structure even when the balloon is deflated and wrappedonto a catheter.

By this process, and unlike balloons formed from coextruded tubing, thelayers 16 and 17 of balloon 20 have been formed with separate stretchratios applied to the tubes 12 and 14 so that optimal strengthproperties can be obtained from both layers.

Multi-laminate balloon structures having three or more laminae can beprepared, for instance, by the additional steps of inserting a compositetubing structure of FIG. 4 into a third extruded tube which is neckeddown onto the outer surface of stretched tube 15 before performing theballoon blowing step. Structures with higher numbers of laminae can beprepared by repetition of these additional steps before blowing theballoon. With such multi-layer laminates it may be desirable to furtherstretch the composite structure of FIG. 4 or any successive compositestretched tubing structure to reduce the thickness of the composite tobe blown and achieve a desired hoop expansion ratio.

An alternative, less preferred process for forming a balloon of theinvention is illustrated in Example 9.

After being blown, the dual element balloon of the invention may beprovided with a stepped compliance curve by annealing the balloon for ashort time after blowing at a pressure at or only slightly above ambientand at a temperature which causes the blown balloon to shrink. Theprocess is described in U.S. Pat. No. 5,348,538. However, the balloonsof the invention are desirably constructed with a greater differencebetween the low pressure and high pressure linear regions of thecompliance curve so that the transition between the two regions resultsin a step-up of diameter of the balloon of at least 0.4 mm. This isaccomplished by blowing the balloon to the larger diameter and thenshrinking to a greater extent than was done in the specific illustrativeexamples of U.S. Pat. No. 5,348,538. The amount of shrinkage iscontrolled by the pressure maintained in the balloon during annealingand the temperature and time of the annealing. The annealing pressure issuitably in the range of 0-20, preferably 5-10 psi at 70-100° C. for 3seconds to 3 hours.

The invention is illustrated by the following non-limiting examples.

EXAMPLE 1

A PET tube was extruded with an inner diameter of 0.0136 inch and anouter diameter of 0.0288 inch from Traytuf 7357 (Shell Chemical, Akron)PET resin. The PET tube was stretched to 2.25× its original length (2.25stretch ratio) at 90° C. The stretched tube was then inserted into atube of extruded polyester-polyether block copolymer resin (Amitel EM740, DSM Engineering Plastics, Evansville Ind.) of 0.0260 inch ID and0.0340 inch OD. The polyester-polyether resin tube was cold necked(stretched at ambient temperature) at 4.0 stretch ratio over the PETtube, without further stretching of the PET tube. The resultingcoaxially arranged tube assembly was then inserted into a 3.0 mm balloonmold and blown. The mold temperature was 97° C. and the blowing pressurewas 350 psi with 30 gms tension applied during the blowing process. Themeasured balloon double wall thickness (i.e. two layers of PET and twolayers of polyester-polyether) was 0.00145 inch, corresponding to asingle wall thickness (one layer each of PET and polyester-polyether) of0.00073 inch. The compliance curve showed balloon growth from 8 to 18atm of 2.6%, and 6.25% from 8 to 28 atm. The balloon burst pressure was529 psi (36 atm). When the balloons prepared in this manner weredissected, the double wall thickness of the PET element was 0.00085 inchand of the polyester-polyether element was 0.0006 inch.

EXAMPLE 2 (Reference example)

An extruded tube of the same Amitel EM 740 polyester/polyether resinwith the same dimension used in Example 1 was made into a single layerballoon having a double wall thickness 0.0006 inch by stretching andblowing the balloon under similar conditions to those of Example 1. Theburst pressure of this balloon was 147 psi (10 atm).

EXAMPLE 3 (Reference example)

A PET tube with the same dimension as used in Example 1 was made into asingle layer balloon having a double wall thickness of 0.00085 inch bystretching and blowing under similar conditions as in Example 1 Theburst pressure of this balloon was 338 psi. (23 atm).

Comparison of the burst strengths of the two reference balloons producedin Examples 2 and 3 with the burst strength of the inventive balloon ofExample 1 shows that the strength of the inventive balloon was more thanthe sum of the strengths of the two reference balloons.

EXAMPLE 4

A PET tube was extruded with an inner diameter of 0.0134 inch and anouter diameter of 0.0325 inch from Traytuf 7357 PET resin. The PET tubewas stretched at a 2.25 stretch ratio at 90° C. The stretched tube wasthen inserted into a tube of extruded Arnitel EM 740 polyester-polyetherblock copolymer resin. The extruded tube had dimensions of 0.0245 inchID and 0.0405 inch OD. The polyester-polyether resin tube was stretchedat ambient temperature at 4.0 stretch ratio over the PET tube, withoutfurther stretching of the PET tube. The resulting coaxially arrangedtube assembly was then inserted into a balloon 3.0 mm mold and blown.The mold temperature was 97° C. and the blowing pressure was 460 psiwith 150 gms tension applied during the blowing process. The measuredballoon double wall thickness was 0.0016 inch, corresponding to a singlewall thickness (one layer each of PET and polyester-polyether) of 0.0008inch. The compliance curve showed balloon growth from 8 to 18 atm of 4%,and 9% from 8 to 28 atm. The balloon burst pressure was 426 psi (29atm). When similarly prepared balloons were dissected, the double wallthickness of the PET element was 0.0009 inch and of thepolyester-polyether element was 0.0008 inch.

EXAMPLE 5

A PET tube was extruded with an inner diameter of 0.0147 inch and anouter diameter of 0.0291 inch from Traytuf 7357 PET resin. The PET tubewas stretched at a 2.25 stretch ratio at 90° C. The stretched tube wasthen inserted into a tube of extruded Arnitel EM 740 polyester-polyetherblock copolymer resin. The extruded tube had dimensions of 0.026 inch IDand 0.043 inch OD. The polyester-polyether resin tube was stretched atambient temperature at 4.0 stretch ratio over the PET tube, withoutfurther stretching of the PET tube. The resulting coaxially arrangedtube assembly was then inserted into a balloon 3.25 mm mold and blown.The mold temperature was 97° C. and the blowing pressure was 500 psiwith 600 gms tension applied during the blowing process. The measuredballoon double wall thickness was 0.0022 inch. The PET layer double wallthickness was 0.0012 inch and the Arnitel layer double wall thicknesswas 0.0010 inch. The compliance curve showed balloon growth from 8 to 18atm of 3%, and 5% from 8 to 28 atm. The balloon burst pressure was 573psi (39 atm). The compliance curve for this balloon is shown in FIG. 6.

EXAMPLE 6 (Reference example)

A tube of Arnitel EM 740 resin with the same dimensions as example 2 wasmade into a single balloon with double wall thickness 0.0007 inch. Theburst pressure of the resulting balloon was 221 psi (15 atm).

EXAMPLE 7 (Reference example)

A PET tube with the same dimensions as example 3 was made into a singlelayer balloon with double wall thickness 0.0008 inch. The burst pressurewas 330 psi (22 atm).

EXAMPLE 8

A PET tube of 0.0147 inch ID and 0.0275 inch OD was extruded fromTraytuf 7357 PET resin. The PET tube was stretched at a 2.25 ratio at90° C. The stretched tube was then inserted into a tube of extrudedArnitel EM 740 resin. Then, the Arnitel tube was stretched at ambienttemperature over the PET tube at a 4.0 stretch ratio, without furtherstretching the PET tube. The combined tube was then inserted into a moldwith body dimension of 3.0 mm. The mold process was similar to thatdescribed in WO95/22367, using a mold temperature of 97° C. and blowingpressure/tension settings (psi/gms) of 530/40, 150/40 and 580/100,respectively, to blow the proximal, body and distal portions of theballoon respectively. The balloon was then shrunk by annealing at 82° C.for 2 hours at 5 psi inflation pressure. The balloon double wallthickness was 0.0018 inch. The balloon had a hybrid or step compliancecurve as demonstrated in FIG. 7. The average balloon burst pressure for3 balloons prepared in this manner was 417 psi (28.5 atm).

EXAMPLE 9

This example illustrates an alternative laminate balloon blowingprocedure of the invention and produces a balloon in which the softflexible polymer is the under layer.

Extruded tubes of PET having dimensions of 0.0136 ID and 0.0288 OD andArnitel EM 740 having dimensions of 0.0210 ID and 0.0370 OD were used inthis example. Single layer PET balloons were prepared by stretching thePET tubes at 2.25 stretch ratio and then blowing the stretched tubes ina 2.8 mm mold using a mold temperature of 97° C. and blowingpressure/tension settings (psi/grns) of 210/20, 100/20 and 210/20,respectively, to blow the proximal, body and distal portions of theballoons respectively. The Arnitel EM 740 tubes were stretched atambient temperature at a 4.0 stretch ratio and each inserted into a PETballoon, still in the mold. The Arnitel tubing was blown at 80° C. and400 psi pressure without applying tension, yielding laminate balloonswhich had an average double wall thickness of 0.0023 inch and an averageburst pressure of 398 psi (27 atm).

Balloons of the invention may be prepared for use on medical devices invarious interventional medical specialties including cardiology,gastroenterology, pulmonary medicine, radiology, urology and vascularsurgery. Examples of useful applications include catheters used incoronary and vascular percutaneous transluminal angioplasty, cathetersused for ultrasound or laser imaging systems, catheters used to deliverand implant vascular prostheses, devices used to diagnose and treatgastrointestinal disorders, biliary interventional products used inendoscopic procedures in the gall bladder and bile ducts, and prostratedilatation catheters. Depending on the particular application, theballoons may be prepared with a wide range of inflated diameters,typically in the range of 1 mm to about 30 mm, and more typically 1.5 mmto about 20 mm, with typical lengths ranging from 5 mm to about 100 mm.

Although the present invention has been described in terms of specificembodiments, it is anticipated that alterations and modificationsthereof will no doubt be come apparent to those skilled in the art. Itis therefore intended that the following claims be interpreted ascovering all such alterations and modifications as fall within the truespirit and scope of the invention.

What is claimed is:
 1. A laminate balloon comprising at least two layersof polymer material which are coextensive over the body of the balloonwhen the balloon is at rest, the balloon produced by a processcomprising the steps of:a) providing a first tubing segment of a polymermaterial; b) stretching the first tubing segment at a first stretchratio to produce a first stretched tube having an outer diameter; c)providing a second tubing segment of a polymer material said secondtubing segment having an inner diameter greater than the outer diameterof the first stretched tube; d) inserting the first stretched tube intothe second tubing segment; e) stretching the second tubing segment at asecond stretch ratio to produce a second stretched tube, the first andsecond stretched tubes being brought into direct annular contact duringthe stretching of said second tubing segment, to form a laminatestretched tubing structure; and f) forming the laminate balloon bypressurizing the laminate stretched tubing structure at a temperatureand pressure above ambient so as to expand the laminate stretched tubingstructure,the balloon so produced having a wall strength which isgreater than each of said layers individually.
 2. A laminate balloon asin claim 1 having a generally linear compliance curve.
 3. A laminateballoon as in claim 1 having a stepped compliance curve.
 4. A laminateballoon as in claim 1 wherein the first and second tubing segments aremade of the same polymer material.
 5. A laminate balloon as in claim 1wherein the first and second tubing segments are made of differentpolymer materials.
 6. A laminate balloon as in claim 5 wherein the firsttubing segment polymer material is selected from the group consisting ofpolyesters, polyamides, thermoplastic polyimides, liquid crystalpolymers and high strength engineering thermoplastic polyurethanes andthe polymer material of the second tubing segment is a thermoplasticelastomer.
 7. A laminate balloon as in claim 6 wherein saidthermoplastic elastomer is a polyester/polyether segmented blockcopolymer.
 8. A laminate balloon as in claim 7 wherein the first polymertubing segment polymer material is PET.
 9. A laminate balloon as inclaim 5 one of said polymer materials is a low compliant, high strengthpolymer and the other of said polymer materials is a relatively softerand more flexible polymer material.
 10. A laminate balloon as in claim 9wherein in said process the first and second stretch ratios aredifferent.
 11. A laminate balloon as in claim 6 wherein in said laminateballoon said first and second tubing segments form respective first andsecond layers, and the wall strength of the laminate balloon exceeds thewall strength of a first reference balloon formed of the same materialas the laminate balloon first layer at a wall thickness, a stretch ratioand a hoop expansion ratio substantially the same as the wall thickness,stretch ratio and hoop expansion ratio of said laminate balloon firstlayer by an amount which is at least 50% of the wall strength of asecond reference balloon formed of the same material as said laminateballoon second layer at a wall thickness, a stretch ratio and a hoopexpansion ratio substantially the same as the wall thickness, stretchratio and hoop expansion ratio of said laminate balloon second layer.12. A laminate balloon as in claim 11 wherein the laminate balloon wallstrength exceeds the wall strength of said first reference balloon by anamount which is at least 75% of the wall strength of said secondreference balloon.
 13. A laminate balloon as in claim 1 wherein theballoon has a nominal diameter in the range of from about 2.5 mm toabout 3.5 mm and a burst pressure of about 27 atm or higher.
 14. Alaminate balloon as in claim 1 wherein in said process the first andsecond stretch ratios are different.
 15. A laminate balloon ascomprising at least two adjacent layers of separately orientedthermoplastic polymer material made of the same polymer material, whichare coextensive over the body of the balloon when the balloon is atrest.
 16. A laminate balloon as in claim 15 wherein the balloon has anominal diameter in the range of from about 2.5 mm to about 3.5 mm and aburst pressure of about 27 atm or higher.